An internal combustion engine of a hybrid vehicle may be started in several ways. For example, an engine may be started via a low voltage starter motor, a belt integrated starter/generator (BISG), or a driveline integrated starter/generator (ISG) that is incorporated into a driveline or powertrain of the hybrid vehicle. However, a low voltage starter motor may unnecessarily increase vehicle cost since the hybrid vehicle may already include a BISG and/or an ISG. Consequently, the hybrid vehicle may be produced with a BISG, BISG and ISG, or only an ISG to start the engine.
At lower ambient temperatures, the hybrid vehicle's available battery output power (e.g., a maximum amount of electrical power the battery may output or source) may be significantly reduced. Further, rotating the engine via the ISG at a desired cranking speed at a low ambient temperature may use significantly more power as compared to rotating the same engine at the desired cranking speed via the ISG at a higher ambient temperature. The hybrid vehicle's battery output power at lower ambient temperature may be insufficient to provide the power to rotate the engine via the ISG at the desired cranking speed at low ambient temperatures.
Likewise, the battery may not have sufficient output to crank the engine via the BISG at lower ambient temperatures. Further, even if the battery has sufficient power to crank the engine at lower ambient temperatures, the BISG may not be able to crank the engine at a desired speed due to belt slippage and capacity of the BISG to rotate the engine at the desired cranking speed at low ambient temperatures.
The inventors herein have recognized the above-mentioned issues and have developed a powertrain operating method, comprising: commanding a motor to a speed via a controller in response to an engine start request; and closing a driveline disconnect clutch via the controller in response to acceleration of the motor being less than a threshold after commanding the motor to the speed.
By commanding a motor to a speed in response to an engine start request and closing a driveline disconnect clutch in response to acceleration of the motor being less than a threshold after commanding the motor to the speed, it may be possible to provide the technical result of starting an engine of a hybrid vehicle at low ambient temperatures. In particular, the motor may be accelerated to a higher speed as compared to if the motor where coupled to the engine and then accelerated. The motor may achieve its maximum speed at its present operating conditions when motor acceleration is less than a threshold. Then, the driveline disconnect clutch may be closed rapidly to transfer kinetic energy and torque from the motor to the engine. The transfer of kinetic energy and torque to the engine accelerates the engine to a higher cranking speed as compared to if the motor and engine were accelerated from zero speed at a same time. Consequently, the engine may be started even when battery output power is reduced due to low ambient temperatures. Further, energy transfer across the driveline disconnect clutch may result in higher energy transfer efficiency as compared to rotating the engine via the BISG.
The present description may provide several advantages. Specifically, the approach may increase the possibility of starting an engine at low ambient temperatures. Further, the approach may provide a useful way to start an engine during conditions of degraded systems. Further still, the approach may reduce the possibility of engine starting system degradation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.